The present disclosure relates to a device and method of stopping an induction motor, and more particularly, to a device for stably stopping an induction motor without a drastic change of output voltage and output current.
There are several methods of stopping an induction motor in rotation.
The several methods of stopping an induction motor include a method of lowering frequency applied from an inverter to an induction motor when the inductor motor is driven (accelerating or reducing speed) using the inverter, and a method of applying DC current to an inductor motor, and a method of reducing frequency while increasing the density of flux occurring in stators of an induction motor.
If described in more detail, one of related art methods of stopping an inductor motor is to lower a frequency applied from an inverter to the induction motor with reference to a predetermined time.
The method uses the following principle. That is, when a conversion amount of a frequency applied to stators is less than a rotational speed of an induction motor in rotation, a slip of the induction motor becomes negative (−), and accordingly, the induction motor slows down due to stopping torque therein.
However, according to this method, the kinetic energy of a rotator in rotation returns to a DC link condenser of an inverter, and accordingly, a voltage of the DC link is increased into a dangerous level.
Additionally, another method of stopping an induction motor is to apply DC current to stators of the induction motor. This method uses the following principle. That is, when DC current is applied to stators of the induction motor, spatially fixed flux occurs due to the DC current flowing in the stators. At this point, once the flux occurs, current induced in the rotator, and, due to the induced current, stopping torque occurs.
That is, when an inductor motor is stopped by using an inverter after operating in a predetermined speed, due to the great inertia of a load, even if output frequency reaches about 0 Hz, the induction motor rotates without stopping, and accordingly, DC current is applied to stators of the induction motor in order to stop the induction motor.
That is, an inverter reduces output frequency in order to stop an induction motor after driving the induction motor at a predetermined frequency. At this point, if the reduced output frequency reaches stopping frequency, in order to apply a predetermined DC current, the inverter applies a predetermined DC current to change a Voltage/Frequency (V/F) driving control mode into a Proportional-Integral (PI) current control mode to use the d-axis and q-axis output of a current controller.
However, as shown in FIG. 1, if the V/F driving control mode change into the PI current control mode during stopping the induction motor, a drastic change in output voltage and current occurs, and due to this, the stopping torque of the induction motor is drastically changed so that stopping performance is deteriorated.